Various methods are known from the prior art to convert first-spectrum images into colour images. A prior art method is described in the article “Natural colour mapping for multiband nightvision imagery” by Alexander Toet, Information Fusion, vol 4 (2003), pp 155-166. In this article, a method is presented to give (fused) multispectral nighttime imagery a natural daytime colour appearance. For input the known method requires a false colour RGB image that is produced by mapping 3 individual bands (or the first 3 principal components) of a multiband nightvision system to the respective channels of an RGB image. The false colour RGB nightvision image is transformed into a perceptually decorrelated colour space. In this colour space the first order statistics of natural colour image (target scene) are transferred to the multispectral nightvision image (source scene). The only requirement of the method is that the colour compositions of the source and target scenes resemble each other to some degree.
The known method is based on equalizing statistical properties (average, standard deviation) of the colours in the multi-band image to that of a reference colour image. An advantage of this method is that a target image can be transformed based on an arbitrary reference colour image. (e.g. colours from a Van Gogh painting can be applied to provide a reference for the transformation).